Radio receiving system



Nov. 10, 1931 F. A. KoLsTER 1,830,948

RADI RECEIVING SYSTEM Filed Feb. 23. 1928 ATTORNEYS Patented Nov. 170, 1931 .Unirse stares FREDERICK a. HOLSTER, or reno ALTO, 'cannon-mn, assitance. To FEDERAL-TELE- PATENT* OFFICE'.

GRAPH COMPANY, OF FRANGSCO, CALIFORNIA, 9e CGR-PRIATEGN OF CALI- FORNIA RADIO REGEIVNG SYSTEM Application led VFebruary 23, 1928." Serial No. 256,101.

This invention relates generally to systems for the reception of signal energy of radio frequency.

Radio receiving systems generally utilize a plurality of vacuum tubes vor electron relays connected together in cascade for'repeating the received or locally modified signalenergy. A number of the electron relays usually function as a multistage radio frequency amplifier, one relay operates as adetector or; integrating device, and theremain'der operate as kaudio frequency amplifiers for supplying a suitable loud speaker or other translating device. Vherc the receiver is made selective over a substantial range of frequencies,as for example a broadcast receiver intended to receive signals within the broadcast range of from 200 to 550 meters,the coupling devices interposed between certain of the electron relays are made selectively tunable and are frequently adjustable manually by means of a.

unitary control. One form of coupling device commonly used consists of an untuned primary coil coupled to a 'secondary coil which is tuned by means of a variable condenser. A receiver of this kind will not have uniform sensitivity over the' entireA wavelength range for which it is adapted kto re-y ceive. When receiving on the lower wavelengths there is a regenerative action which makes the receiver more sensitive than for the longer wave-lengths, while for the wavelengths along the middle of the range, the receiver has good sensitivity. St-rongregenera .l

It is an object of this invention to devisev uniform sensitivity of a radio'receiver..

It is a further objectk o-f this invention to devise means which may be.V interposedsbe- .tweenvthe source vof signalenergy and the :devise means. which may be interposed 'be- .tween a source of signal energy and tlierst electron relay stage of the-radio receiver for compensating for the non-uniform characteristic of the receiver and also for rendering Athe receiverimmuneto-changes inthe electrical .charactristics of the source of energy. Referring to the drawings:

-Figure 1- is a circuit diagram of a radio system incorporating the system of this invention. I p

2 is a detail circuit `diagram of one of the system of Fig. 1.

-Fig. 3 is a detail diagram illustrating the operation of the electrical device lcoupling the antenna circuit tothe first electron relay4 of theA system of Fig. 1. Y Fig. 4 is a detail diagram illustrating an the radio frequency amplifiers employedv alternative arrangement to that shown in Fig. 3.. Y

Fig. 5 comprises curves drawn toillustrate the nature of the reactances ofthe coupling device shown in Figs. 1 and 3. .A

Fig. v6 comprises curves illustrating the nonsuniform characteristic of a receiver andthe manner in which it is compensated.

`Thesystem of my invention may be outlined brieiiy as comprising a radio receiver vwhich utilizes a cascade radio 'frequency amplifier selectively tunable over a substantial wave-length range. Interposed between the first stage of the amplifier and the radio antenna or other source of signal energy', is an .electron relay of the three element type, and the` grid or input circuit' of this relay is connected to .the antennal thru a special compensating coupling device. This coupling device is constructed so lthat Without physical nadjustment it will tendV to automatically compensate for the non-uniform response charsimple means forcompensating for the noni Current from the last amplifier stage is applied to a suitable detector or integrating device 14, the output of which may be repeated thru a single or multistage audio frequency amplifier 15 and impressed upon a suitable loud speaker or translator 16. In accordance with the usual practice in such receivers, I have shown tuned coupling devices 18 for coupling the first amplifier stage l1 to a source of signal energy, for coupling the amplifier stages together, and for coupling the last stage 18 to the detector 14. These coupling devices are preferably of simple construction, comprising for example primary and secondary inductances 19 and 21, the secondary inductance being tuned by means of a variable condenser 22. Each variable condenser forms what may be termed a variable *tuning element and these elements are preferably mechanically interconnected to a unitary control so that they may be simultaneously tuned by an operator. vWith a receiver of this kind all of the amplifier stages are kept in resonance bv the unitary control, and by adjustment of this control the receiver may be selectively tuned to receive any one frequency within a given wavelength range. i

One stage of the radio frequency amplifier is shown in Fig. 2. Iy have shown the electron relay 23 of that stage connected to the secondary of a preceding coupling device 18, and its plate circuit connected to the primary coil of a succeeding` coupling device. Because of the inherent grid plate capacitance of the electron relay. and because of intermagnetic coupling between the input and output circuits, an amplifier constructed in this manner tendsto oscillate locally and to become unstable when tuned to relatively low wave-lengths, since feed back action is more pronounced upon the shorter than upon the longer wavelengths. Although it is unstable at the low wavelengths the amplifier is more eflieient due to regenerative action, and thus the receiver is more sensitive when tuned to the shorter wave-iengt'hs than when tuned to Vthe longer wave-lengths. In other words the receiver has a non-uniform response characteristic.

Since instability in a receiver is an undesirable feature, I preferably provide means for minimizing the same, as for example a resistance 24 inserted .in series with the grid of each of the radio frequency amplifier tubes 23. This introduces a resistance component in the relay circuits which tends to decrease the tendency of the cascade radio frequency amplifier as a whole to oscillate and reduces regeneration. The corresponding reduction in regenerative action however reduces the sensitivity of the receiver at the shorter wave-lengths. Such a receiver will have a response curve somewhat as shown by the curve 1 of Fig. 6, which has been plotted for the broadcast wavelength range of from 200 to about 550 meters. As indicated by this curve the response of the receiver has a drooping characteristic at both limits of the wavelength range. The loss in sensitivity at the llonger wave-lengths is due in part to the characteristics of the coupling devices 18.

In accordance with this invention I provide means for increasing the sensitivity of the receiver at both limits of the wave lengthrange, without however rendering the receiver unstable because of regeneration. As shown in Fig. 1 the particular means which I employ includes an additional electron relay 26 having its output circuit connected-L to the coupling device 18 in the input circuit of the amplifier 11, and having its input or grid circuit associated with a suitable source of signal energy by means of a special coupling device 27. The source of energy hasA been indicated as comprising a radio antenna 28 andV ground connection 29. The coupling device 27 is so designed as to give different impedance effects at different frequencies, whereby in effect more efficient transfer ofenergy is secured from the antenna relay 2G for frequencies near the limits of the wavelength range, than for frequencies lying betweenl the limits.

In one specific embodiment of my inven!v tion, device 27 comprises two branch paths for currents flowing in the antenna circuit, one path being formed by the inductance L1, and the other path being formed by the inductance L2 and a capacitance G2 in series with inductance L2. For the capacitance C2 I prefer to utilize the inherent grid-cathode capacitance of the relay 26. Inductances L1 and L2 are so selected and proportioned, that the combination of elements reaches or approaches a condition of resonance near each limit of the wave-length range for which the receiver is adapted to operate.

To explain the design and mode of operation of the coupling device 27, reference is made to Fig. S in which a capacitance C3 has been'substituted for the capacitance of the antenna 28, the inductance and resistance of the antenna circuit being ignored for purposes ofexplanation. `This arrangement has two different periods of freedom or points of resonance. At one resonant frequency current may be considered as flowing thru capacitance C3 'and vthru inductance L1 and react-ance LZCZ taken in parallel. At another resonant frequency circulatory current flows between inductance L1 and the reactance formed by L2C2. This effect may be more clearly explained by referring to the curves` of Fig. 5. Curve 2- indicates the reactance of the arrangement considering L1 and LZGZ asa unit shunted by capacitance C3. kAs shown this arrangement has a resonant point at the wave-length indicated by the dotted line 32 which is selected near the lower frequency limit of the wave-length range. Preferably this resonant point lies outside of the wave-length range and for-this reason line 32 in the illustration occupies approximately the 60() meter point corresponding to the broadcast range of 200 to 550 meters. Curve number 3 indicates the reactance of the arrangement sliown in Fig. 4 comprising L2 and C2 in series shunted by capacitance C3. The reactance of this arrangement is preferably made negative throughout the wave-length range and increases negatively from the shorter to the longer wave-lengthV limits. At some point near the lower wave length limit, say for example at a wave-length of about 175 meters indicated by dotted line 33, there is also a condition of resonance since the positive reactance indicated by curve 2 is equal to the negative reactance of curve 3. In other words distance a is equal to distance Thus a condition of resonance will be attained or approached near each limit of the wavelength range for the arrangement sho-wn in Fig. 3. Y

When the input circuit of relay 26 is connected across to the capacitanceV C2, as in the arrangement shown in Fig. 1, it is obvious that tlie transfer of high frequency energy from the antenna to the relay will be most effective near the two resonant points ofthe circuit arrangement vshown in Fig. 3.

` lay 26 than at wave-lengths lying along the middle of the wave-length range. Thus the device 27 taken with the relay 26 will have non-uniform sensitivity for different selected frequencies, but this non-uniformity is-ot1 such a character as to compensate for the non-uniformity of the receiver.

wave-lengths. The resulting system nowxlias more nearly uniform sensitivity over the entire wave-length range. It is to be noted however that this uniform sensitivity is not obtained by sacrificing stability, since the operation of the radio frequency'ampliiier of the l receiver still has a sensitivity characteristic Inr other words near the limits of the waveindicated bythe dotted line-33 (Fig. 5) outside the wave-length range, altho the resonant point at" the other limit of thewavelength range indicated by line 32 may fall within rather than without the wave-length range. The exact location of these resonant points'with respect to the wave-length range depends somewhat upon the characteristics of the receiver supplied by the relay 26.

VThe system as explained above possesses another important advantage in that .the operation of the receiver is practically unaffected by changes in the electrical characteristics of the antenna 28. The system may be connected to antennae of different lengths and different electrical characteristics, Vwithout making an individual compensating adjustment for the tuning of the first coupling device 18. Thus a definite-movement may be imparted to thecondenser 22 of the first coupling device 18'by the unitary control, and this movement may remain exactly the same with respect tothe `other condensers 22l irref spective 'of the naturefof the antenna being used. This feature is especially desirable with broadcast vreceiving sets since with my invention they may beiinally adjusted at` the factoryand will-operate with good efi- .1

ciency when connected to a variety of antennae. The capacitance C2 ismade assmall as possible, so that capacitance C3 representing vthe antenna ground capacitance, is Arelatively large 'in proportion. Thus while varii material effect upon the voverall uniformity of the system. A small capacitance may be shunted vacross the grid and filament of relays 26 to supplement the grid cathode capacitance of this relay, but in any event'the capacitance Y C2l should be kept relatively small. y f Y Y I prefer in practice to introduce a substantial resistance in series with inductance L2 and `caitiacitanceg-Ca For example this resistance' may be' formed by Awinding a coil of resistance wire to form. the inductance L2. Resist-ance introduced in the series with L2 has the effect lof broadening the high frequency ,resonant peak of the coupling device 27, but has little effect upon the longer wave length resonant peak.. vBy the use of resistance in this manner, I am enabled tov malre the curve 4 more neaily linear near the lower wave-length limit and thus to prevent any .possible instability of the relay 26 when the receiver is operated at low wave-lengths.

I claim: 1. In a system for thereception of signals 'of-carrier, frequency, a source of signal energy, amplifying and translatingineans havingnon-uniform sensitivity for differentcarrie'r frequencies impressed upon the same,

' and means interposed between the source and said amplifying and translating means for repeating signal energy from said source into said amplifying' and translating means, said last named means having non-uniform sensitivity for different carrier frequencies of a character tending to compensate for the nonuniform 'sensitivity of the amplifying and translating means.

2. In a system for the reception of signals of carrier frequency, a source of signal energy, a radio frequency amplifier, detecting and translating means receiving energy from the amplifier', said cascade amplifier having non-uniform sensitivity for. signal energy of different frequencies, and mea-ns .interposed between the'source and said.- amplifier for repeating signal energy from said source to said amplifier, said last named means having non-uniform sensitivity for signal energy of different frequencies but of a character tending tocompensate for the, norfunifoim sensitivity of the amplifier.

8. In a system for the reception of signals of carrier frequency, a source of signal energy, a. radio frequency amplifier, detecting and translatingV means receiving venergy from the amplifier, said cascade amplifier `having non-uniform sensitivity for signal energy of different frequencies, and means including an electron relay interposed between the source and said amplifier for repeating signal energy from said source to said amplifier, said-last named means having non-uniform sensitivity for signal energy of different frequencies but ofv a character tending to compensate for the non-uniform sensitivity of the amplifier. i

Il. In a system for the reception of signals of carrier frequency. a source of signal energy, a radio frequency amplifier, detecting and translating means receiving energy from the amplifier, said cascade amplifier having non-uniform sensitivity for signal energy of different frequencies, an electron relay having its outputcoupled to the input of said amplifier, and reactive means coupling said source with the input of said relay for causing said relay tor have non-uniform sensitivity for signal energyl of different fre'- quencies received from said source, the nonuniform sensitivity of said relay being of such a character as to substantially compensate for the non-uniform sensitivity of the amplifier.

5.V In a system for the reception of signals of carrier frequency, a source of signal energy. a receiver including a plurality of electron relays coupled in cascade andA having a plurality of individual tuning elements simultaneously variable by a unitary control whereby thereceiver may be selectively tuned over awide range of radio frequencies by movement ofsaid unitary control, said receiver having a non-uniform response characteristic for energy of differentv frequencies, and meansinterposed between said receiver and said sourcefor preventing changes in the constants of said individual timing elcments due lto variations in the electrical properties of said source, said means serving to repeat signal energy from said source to the receiver in such a ymanner as to compensate for the non-uniform response character- -istic of the receiver.

6. In a system for the reception of signals of carrier frequency, a source of signal energy, a receiver including a plurality of electron relays coupled in cascade and having a plurality of individual tuning elements simultaneouslyvariable by a unitary control whereby the receiver may be selectively tuned over a wide range of radio frequencies Vby movement of ysaid unitary control, said receiver having a non-uniform response characteristic for energies of different frequencies, and means interposed between said receiver and said source for renderingsaid individual tuning elements independent of variations in the electrical properties of said source, said mea-ns comprising an electron relay having its output circuit coupled to the input circuit of the receiver, and a plurality of reactive elements associated with the input circuit of said relay and the source of signal energy, said elements being so arranged as to automatically vary the effective electrical coupling between said source and said relay in accordance with a variation in the frequency of signal energy, said variable electrical coupling serving to compensate for the non-uniform .response characteristic of the receiver.

7. In a systemfor the reception of signal energy of carrier frequency, a source of signal energy, an elect-ron relay having an anode, a cathode, and a grid controlling the space charge between'the anodeand cathode, said relay having an effective grid-cathode capacitance, a cascade 'electron relay system coupled to the output of said amplifier, a plurality of reactances arranged to form parallel paths for current received from said source, each of said paths including at least one inductive element, and one of said paths including a series capacitative element formed at least in part by the grid-cathode capacitance ofthe relay, said elements being so proportioned and related as to provide a device which affords a variation in the effective electrical coupling between the source and said relay in accordance with avariation of the frequency of incoming signals and without physical adjustments.

8. In a system for the reception of signals of carrier frequency, a receiver selectively tunable over al substantial wave-length range and having a greater response at wave-v lengths near the middle of said range than near the ends, a source of signal energy, and coupling means interposed between Said source and said receiver, said coupling means having two points of resonanceat frequencies lying adjacent theV limits of said wave length range.

9. The combination of a high frequency amplifier tunable over a range of frequencies and having greater sensitivity at frequencies near the middle of said range than near the ends thereof, with an input circuit coupled thereto by a uni-directional translating device, said input circuit comprising a reactance element in shunt to said uni-directional translating device and other reactance elements constituting with said first reactance element a resonant circuit at frequencies adjacent the limits of said range.V

10. The combination of a high frequency amplifier tunable over a range of frequencies and having non-uniform sensitivity over said range with an input circuit therefor comprising acapacit element eectively in shunt with saidl ampli er, a first inductance and a second inductance in series with said capacity element and a second capacity element larger than said first capacity element in shunt to one of said inductances.

l1. A radio frequency amplifier tunable over a range of frequencies and having nonuniform sensitivity over said range, a signal energy input device and means interposed between said amplifier and said input device to modify the eiiiciency of the latter compensatively with respect to the sensitivity of said amplifier for different frequencies.

12. A signal energy absorption device in association with reactances causing the same to have two resonance points, an amplifier network the sensitivity of which tends to i vary throuvhout the operating range of frequencies of signal energy inversely to the resonant characteristics of said absorption device in association with said reactances, and a thermionic relay interposed between said reactances and said amplifier network.

In testimony whereof, I have hereunto set my hand.

FREDERICK A. KOLSTER.

DISOLAIIVI ER 1,830,948.-Fredericlc A. Kolster, Palo Alto, Calif. RADIO RECEIVING SYsTEM. Patent dated November 10, 1931. Disclaimer filed October 23, 19811, by the assignee, Federal Telegraph Company.

Hereby enters the following disclaimer:

In claim 1, no claim is made to the combination recited except where the means interposed between the source and the amplifying and translating means is resonant at a frequency near the lower end and at a frequency near the upper end of a frequency range containing the different carrier frequencies.

In claim 2, no claim is made to the combination recited except where the means interposed between the source and the amplifier is resonant at a frequency below the lower end and at a frequency near the upper end of a frequency range containing the different carrier frequencies.

In claim 3, no claim is made to the combination recited except where the electron relay has no tunable element in its input circuit.

In claim 4, 'no claim is made to the combination recited except where the input of the electron relay contains no tunable element.

In claim 5, no claim is made to the combination recited except where the means is resonant at a frequency below the lower end and at a frequency above the upper end of the range.

In claim 6, no claim is made to the combination recited except where the input circuit of the electron relay contains no tunable element varied by the unitary control.

In claim 11, no claim is made to the combination recited except where the means is resonant at a frequency near the lower end and at a frequency near the upper end of the range.

[Oficial Gazette November 1S, 1934.] 

